1. Field of the Invention
The present invention relates to an ATM network device and more particularly to an ATM network device capable of allocating a previously ensured (cached) channel with respect to a connection setting request given from a terminal.
2. Related Background Art
A method of setting a connection in an ATM (Asynchronous Transfer Mode) is classified into a PVC (Permanent Virtual Channel) for permanently setting a path and an SVC (Switched Virtual Channel) for dynamically setting the path.
The PVC is usable without an occurrence of overhead for setting the connection because of the connection remaining set. There is, however, such a defect that resources of the whole network can not be effectively utilized, because a QOS (Quality-of-Service) and a line bandwidth remains fixed.
Contrastingly in the SVC, although there might occur the overhead for setting the connection, the QOS and the bandwidth to be used can be freely set, and a route within the network can be changed with a flexibility corresponding to a traffic. If short-time communications frequently occur, it might take much overhead time for setting the connection, and consequently a proportion of the connection setting time to a content transfer time becomes large.
As explained above, the PVC and the SVC have their own merits and demerits and used separately corresponding to purposes of the connections. For instance, if the ATM is used in a public network used by users requiring a diversified applications, the connections are set as the SVC.
By contrast, if the ATM network is utilized as a backbone for an INTERNET or an INTRANET, it can be considered that there might always occur a request for setting the connections having the same connection attributes (the QOS, a using bandwidth and a terminal to be connected, etc). In such a utilizing condition, there becomes a smaller load upon the network by setting the connection as the PVC.
Even in such a using condition, however, the bandwidth of each PVC is set corresponding to a traffic peak, and therefore, if the traffic largely fluctuates depending on the time, a large-capacity physical line corresponding thereto must be ensured. Accordingly, a tremendous investment must be put into the network resources.
Even so, when the connection is set based on the SVC, it follows that the request for setting the connections exhibiting absolutely the same attributes is repeated many times at a high-traffic time despite becoming flexible to the traffic fluctuations, with the result that a processing load on the whole network becomes large.
To overcome the above-described problems, it is a primary object of the present invention to provide an ATM network device capable of actualizing merits of both of an SVC and a PVC, effectively utilizing resources of a whole network by releasing connections when a traffic congestion is small, and besides, even if a request for setting the connections having absolutely the same attribute is repeated any number of times, decreasing an overhead time.
The ATM network device according to the present invention adopts following constructions in order to obviate the problems described above.
According to a first aspect of the present invention, an ATM network device comprises an ATM switch unit in which a connection for transmitting an ATM cell having a specified identifier through a predetermined interface is set, a message receiving unit for receiving via the ATM switch unit a call control signaling message transmitted from outside, a connection information retaining unit for retaining, per connection, connection information which specifies the connection set in the ATM switch unit, and indicates whether the specified connection is in an activated state or in a halt state, a connection management unit which makes, when a call control signaling message received by the message receiving unit indicates a request to release a connection from a call, a change so that the connection information specifying the connection of which release is requested indicates the halt state, also making, when a call control signaling message received by the message receiving unit indicates a request for setting a connection for another new call, a change so that any piece of connection information indicating the halt state indicates the activated state, and allocating a connection specified by this piece of connection information to the new call.
With this construction, when the call control signaling message indicating a request for setting a connection is transmitted from a terminal, the connection management unit checks whether or not there exists the connection information which indicates the halt state among pieces of connection information retained by the connection information retaining unit. Then, if there exists the connection information indicating the halt state, the connection management unit allocates the connection specified by the connection information indicating the halt state to the call which is requested to be set with a connector through the call control signaling message, and changes the connection information on the allocated connection so as to indicate the activated state. Thereafter, when the call control signaling message indicating a request to release the call from the connection is transmitted from the terminal, the connection management unit changes the connection information specifying the connection of which release is requested so as to indicate the halt state. Thereafter, when the call control signaling message indicating the request for setting the connection is transmitted from the terminal or another one, the connection management unit allocates the connection of which connection information indicates the halt state, to a new call which is requested to be set with a connection through this call control signaling message. Thus, the connection set in the ATM switch unit continues to be cached by the connection information in the connection information retaining unit. As described above, it might be sufficient to simply allocate the connection in response to the connection setting request, and hence there occurs a less amount of overhead than by newly setting the connection. Further, the connection is brought into the halt state with respect to the connection release request, however, the connection set in the halt state is allocated to other call, whereby the resources of the whole network can be effectively utilized.
According to a second aspect of the present invention, in the ATM network device according to the first aspect, the connection information indicates an identifier used for the specified connection, and the connection management unit allocates the connection to the new call by imparting the identifier used for the connection to the ATM cell belonging to the call.
According to a third aspect of the present invention, in the ATM network device according to the first aspect, if there is no connection information indicating the halt state when the call control message received by the message receiving unit shows the request for setting the connection for the new call, the connection management unit sets a new connection in the ATM switch unit, and allocates this new connection to the call.
With this construction, the new connection can be set.
According to a fourth aspect of the present invention, in the ATM network device according to the third aspect, when newly setting the connection in the ATM switch unit, the connection management unit registers the connection information retaining unit with new connection information specifying the newly set connection.
When thus constructed, even if the new connection is set, this new connection can be managed through the connection information, and it is therefore feasible to set the connection in the halt state when the release of the connection is requested and to allocate the connection to other call.
According to a fifth aspect of the present invention, in the ATM network device according to the fourth aspect, the connection information retaining unit further retains upper limit bandwidth information defining an upper limit of a total sum of bandwidths of all the connections specified by the respective retained pieces of connection information, and the connection management unit registers the connection information retaining unit with the connection information specifying the newly set connection as far as the total sum of bandwidths of all the connections specified by the respective pieces of connection information retained by the connection information retaining unit, falls within the upper limit defined by the upper limit bandwidth information.
When constructed in this way, since the registration of the new connection can be restricted, it is possible to ensure a room for enabling the connection to be newly set with respect to a call to which the connection kept in the halt state can not be allocated for the reason of a difference between the connection attributes etc.
According to a sixth aspect of the present invention, in the ATM network device according to the fourth aspect, each piece of connection information indicates an attribute of the specified connection, the connection information retaining unit further retains per classification of the attribute the upper limit bandwidth information defining the upper limit of the total sum of bandwidths of the connections specified by the respective retained pieces of connection information, and the connection management unit registers the connection information retaining unit with the connection information specifying the newly set connection as far as the total sum of bandwidths of the connections specified by the connection information indicating the same attribute as that of the newly set connection, falls within the upper limit defined by the upper limit bandwidth information on this attribute.
If thus constructed, the upper limit of the bandwidth can be set per connection attribute, and hence an elaborate connection management can be done.
According to a seventh aspect of the present invention, in the ATM network device according to the first aspect, the connection information retaining unit further retains release condition information indicating a condition for releasing the connection specified by the retained piece of connection information, and the connection management unit deletes any one piece of connection information out of the connection information retaining unit in accordance with the condition indicated by the release condition information.
With this construction, it is feasible to release the connection of which connection information needs not to be registered, whereby the resources of the whole network can be effectively utilized.
According to an eighth aspect of the present invention, in the ATM network device according to the first aspect, each piece of connection information indicates an attribute of the specified connection, the connection information retaining unit further retains per classification of the attribute the release condition information for indicating a condition for releasing the connection specified by the retained piece of connection information, and the connection management unit deletes any one piece of connection information out of the connection information retaining unit in accordance with the condition indicated by the release condition information.
When constructed in this manner, the release condition can be set per connection attribute, and therefore the elaborate connection management can be performed.
According to a ninth aspect of the present invention, in the ATM network device according to the first aspect, after the message receiving unit has received the call control signaling message for indicating a request to release a connection from a call, and when the ATM cell belonging to this call flows into the ATM switch unit, the connection management unit releases the connection having been allocated to this call.
If thus constructed, it is possible to effectively prevent the user from an invalid utilization of the connection.
According to a tenth aspect of the present invention, in the ATM network device according to the first aspect, the connection set in the ATM switch unit is a permanent virtual channel set between two ATM networks.
According to an eleventh aspect of the present invention, in the ATM network device according to the first aspect, the connection set in the ATM switch unit is a switched virtual channel set with respect to other ATM network.
According to a twelfth aspect of the present invention, the ATM network device according to the eleventh aspect may further comprise a message transmitting unit for transmitting a message for requesting the connection management unit of the other ATM network device to change, when the connection management unit has changed a connection information for specifying a connection so as to indicate the halt state, a connection information for specifying the connection so as to indicate the halt state, and transmitting a message requesting the connection management unit of the other ATM network device to change, when the connection management unit has changed a connection information for specifying a connection so as to indicate the activated state, a connection information for specifying the connection so as to indicate the activated state.